The journeyman right-hander from Venezuela barely touches 90 mph with his fastball, and he hasn't won more than four games in any of his seven seasons in the majors.

But when Petit takes the mound against the Colorado Rockies on Thursday, replacing the struggling Tim Lincecum for at least one start, he will be carrying a streak that goes well beyond the 27 consecutive outs required for a perfecto. Furthermore, less than a year ago he took his own bid for immortality even further than Bumgarner's seven spotless innings.

Petit, 29, has retired the last 38 batters he has faced – over seven outings – just seven short of the record set by Mark Buehrle with the Chicago White Sox in 2009. Petit's streak, which he didn't know about until recently, is tied for the sixth longest ever.

It's an unlikely accomplishment for a pitcher with a career 4.84 ERA who spent the 2011 season with the Oaxaca Warriors of the Mexican league. For that matter, so was his near-perfecto against the Arizona Diamondbacks on Sept. 6, spoiled by Eric Chavez's two-out single in the ninth.

Both achievements speak to Petit's growth as a pitcher and his ability to adapt. Teammate Pablo Sandoval first faced Petit in 2009 and pointed out he's very different now.

"He didn't know how to pitch before,'' Sandoval said, "and I think what helped him get back here was pitching in the Mexican league, which has a lot of veterans. You need to know how to pitch in that league.''

And at the major league level, you need to establish your fastball. That's something Petit was reluctant to do early in his career, when he bounced around between the then-Florida Marlins, the Diamondbacks and the minors.

Starting in 36 of his 71 games from 2006-09, Petit compiled a 10-20 record with a 5.57 ERA. He spent 2010 in the minors and nearly all of 2012 as well, plus the 2011 season in Mexico. As a long reliever and spot starter for the Giants the last two years, Petit has gone 7-4 with a 3.58 ERA in 41 games, 13 of them starts.

"I'm not known for having an overpowering fastball, and in today's baseball a 95 mph fastball is average. I don't get it up there,'' Petit said in Spanish. "Sometimes in (his earlier days) I would be afraid to throw my fastball, so I would throw the wrong pitch, and that's why I failed so much. Now I only think about attacking the strike zone. If they get a hit off me, I'll try to get a double play. I've developed a lot of confidence in my fastball.''

That pitch is most effective when he mixes it with his cutter, curve and changeup, which helps keep hitters off-balance. Petit said he hasn't been doing anything different during his streak, but simply focusing on getting ahead in the count.

Once he does, the results can be impressive. Petit struck out five of the six batters he faced Aug. 19 against the Chicago Cubs, and another five in 4 1/3 innings Saturday against the Washington Nationals. For the season, he has struck out 87 and walked 17 in 80 1/3 innings, all the while staying comfortably below the major league average velocity.

"It's the hardest 88- or 90-mph fastball I've ever seen,'' said Rockies third baseman Nolan Arenado, the NL's reigning player of the week. "He mixes in that cutter and that slider really well. It's really hard to pick up.

"I faced him last year as a starter and he was good too, but now in the bullpen he's even tougher because you only see him once in a while, and you don't know what he's going to throw you. When you feel like something's coming, that's definitely not the pitch that's coming.''

Petit's challenge will be to carry his bullpen success to the rotation. He went 4-1 with a 3.59 ERA in seven late-season starts last year, but this season he's 1-2 with a 6.32 ERA in six starts. In 27 relief appearances, he has a 1.84 ERA with 59 strikeouts in 49 innings.

Does he have a preference?

"I've learned in this baseball that you can't have a preference,'' Petit said. "You can't be capricious, because in baseball, the more you want something, the less you get it.''

Manager Bruce Bochy dismisses the notion that Petit may lose effectiveness once hitters see him a second or third time, pointing to his strong showing as a starter last year. The Giants, battling to hold on to a wild-card spot, hope he can reprise that performance in replacing Lincecum, who registered a 9.49 ERA in his last six starts before being shifted to the bullpen.

"Sometimes these guys find it with their delivery and their location,'' Bochy said. "He (Petit) looks like he's in a good place right now with how he's throwing the ball.''

When he became the 12th pitcher in history to lose a perfect game with two outs in the ninth inning last season, Petit still had his first career shutout and first complete game as consolation, finishing the masterpiece in 95 pitches.

He said the feeling he's had on the mound during his last several relief appearances has been quite similar to that magical night.

"I've been working fast, getting quick outs and throwing strikes,'' Petit said. "You try to keep the team in the game, which is very important to have a chance to come back and win. I've been happy with the work I've been doing lately.''